1. Field of the Invention
This invention relates generally to high mast lighting structures, and more particularly, to releasable means for locking and supporting an illumination assembly at the top of such structures.
2. Description of the Prior Art
High mast lighting structures are used for area lighting such as in large parking areas, at highway interchanges and the like. These structures generally include a very tall mast with illumination devices mounted at the top thereof. Servicing of the illumination devices and related structure is difficult because of the great height at which these elements are positioned above the ground. For this reason, such structures generally include means to lower the illumination devices to the bottom of the mast so as to enable convenient servicing thereof at ground level. After the illumination devices have been serviced at the bottom of the mast, they must be raised and locked at the top thereof so that the lighting structure may function in accordance with its intended purpose.
Many devices are known to enable raising and lowering of illumination devices and locking thereof at the top of relatively high masts. Such devices generally include elaborate guiding and control arrangements as well as locking means which are operable to raise the illumination device and to secure the same on the mast. Illustrations of such devices are disclosed in U.S. Pat. Nos. 3,801,813 and 3,805,054 which include a cable assembly to raise the illumination device on the mast and latch means to lock the illumination device. A separate cable connected to the latch means is operable at ground level to release the latch so that the illumination device may be lowered. The necessity for a separate latch release cable gives rise to possible tangling of cables in the restricted area within the mast through which the operating cables must pass.
Illustrations of devices which eliminate the need for a separate latch release cable are found in U.S. Pat. Nos. 3,673,403, 3,721,816, 3,856,639 and 3,862,744. These patents disclose locking apparatus which are operable and releasable at the top of a high mast without a separate latch release cable. Generally, the structures involved include cam members which engage latches when the illumination assembly is moved to the top of the mast, and which are disengageable upon a further movement of the illumination assembly by operation of its hoisting cable at the bottom of the mast. The use of camming members to operate latch members gives rise to further operability considerations. Such latch members must be self-centering as the illumination assembly is moved to the top of the mast; they must be relatively insensitive to misalignment to prevent jams is alignment is not exact; they must be operationally reliable and easily serviceable if repair is needed; and they must be of relatively moderate cost to be desirable for inclusion in high mast lighting systems.
The structure of the present invention provides a locking device which is operable without a separate release cable and yet accomplishes the other objectives of such a device.